Kitchen utensils, for example, cookware such as boilers and the like, have been developed rapidly, which were early made of iron, aluminum or ceramic and gradually superseded by stainless steel that mainly consists of Cr18Ni9. It is well known that early iron kitchenware is magnetic and prone to rust. Later-developed aluminum one is easy to manufacture and nonmagnetic, however, it should be under surface chemical treatment and oil injection during the manufacture process to obtain certain hardness and prevent it from oxidation, meanwhile, the inner surface of this kitchenware should be sprayed with a nonstick coating so that it can be used safely. Cr18Ni9 ( steel type No. 304, called material SUS304 for short bellow) is a kind of Austenitic Steel, whose chemical composition (WT %) comprises: Cr 17-19, Ni 8-11, C≦0.06, Si≦1.00, Mn≦2.00, S≦0.030, P≦0.035, and the balance of Fe. This material is nonmagnetic, corrosion proof and easy to manufacture. Furthermore, its products are antirust so that the surface is shiny and beautiful, and can be used in a gas furnace or an electric cooker. A compound base should be added to the bottom of the products when they are used in induction cookers.
Induction cooker, which makes use of the electromagnetic effect to heat is a stove developed rapidly recently. Since only magnetic materials could be applied in the induction cooker, generally speaking SUS304 itself does not conform to the manufacture of the products used for induction cooker. However, due to its excellent property in many aspects, this material can be made into cooking vessel used for induction cooker if the bottom of the vessel is necessarily covered with magnetic materials. At present, for example, the steel-aluminum-steel compound base is in common use, that is, first a layer of aluminum or copper is soldered on the bottom of the vessel made of the said material; and then a magnetic stainless steel layer is formed on. The material of steel-aluminum-steel, however, costs high and is hard to process. FIG. 1 shows the schematic view of the compound base, wherein material 304 can be used in part A; pure aluminum or copper can be used in part B; and in part C magnetic metal materials, such as steel 1Cr17 (called SUS430 for short, whose chemical composition comprises Cr 16-18, C≦0.12, Si≦0.80, Mn≦0.80, S≦0.030, P≦0.035, Ni≦0.60, trace amount of Mo and Ti, and the balance of Fe) and copper etc., can be used.
In order to solve the problem that SUS304 can not be directly used in the induction cooker, people have been looking for a multifunctional material to substitute for SUS304, which has the advantages of SUS304 and can be applied in manufacture of the products used in the induction cooker, but always failed. In addition, many materials, such as SUS430, perform badly in manufacture process. It certainly will increase the product cost and bring other problems, especially in the manufacture of deep-drawing vessels and containers. As a result, many researchers gave up with no suitable material being found.
SUS436L, which is a kind of Ferritic Steel, comprises in chemical composition (wt %) Cr 17-19, C≦0.025, Si≦1.00, Mn≦1.00, N≦0.02, Ni≦0.60, Ti≦0.75, Mo 0.75-1.50, and the balance of Fe. There is little nickel in this material, meanwhile, trace amount of molybdenum and titanium are added in. This material which is mainly used in automobile silencer and exhaust pipe has excellent anticorrosive property and high heat conductivity and magnetoconductivity.